1. Field of the Invention
The instant invention generally relates to an improved process for producing N-(substituted) morpholine compounds from the corresponding N-(substituted) diethanolamine compound, and, more particularly, to an improved liquid phase process for selectively producing N-alkyl morpholine or N-(hydroxyalkyl)morpholine compounds in the presence of certain specific catalytically effective substances.
2. Prior Art
N-alkyl morpholine compounds are well known polyurethane catalysts. N-(hydroxyalkyl)morpholine compounds are used, for example as a base in pharmaceutical applications, a catalyst for polymerizing vicinal epoxides, a polymer modifier and stabilizer, a textile phosphorescent brightner, i.e. dye accepter and as a starting product for producing bis-(morpholino-N-alkyl) ether compounds which have well known utility as polyurethane catalysts.
N-alkyl morpholines are generally prepared by reaction of an alkanol with morpholine. N-(hydroxyalkyl)morpholine compounds are generally prepared by reaction of morpholine with an alkylene oxide. Morpholine in turn is prepared by various methods, such as, for example, the reaction of diethylene glycol and ammonia over a nickel catalyst at high temperatures and pressures. The disadvantages of such stepwise processes for the preparation of N-(substituted) morpholine compound is readily apparent.
Another known method for preparation of N-alkyl morpholine involves the cyclic dehydration of a corresponding N-(substituted) diethanolamine with stoichiometric amounts of concentrated acid such as hydrochloric, sulfuric and the like with a subsequent neutralization and salt recovery step. A known method for producing N-(2-hydroxyethyl)morpholine from triethanolamine is disclosed in T. Ishiguro, E. Kitamura u. H. Ogawa, J. Pharm. Soc. Japan 75, 1367 (1955); C. A. 50 10106.sup.c (1956). The process involves initially forming a triethanolamine hydrochloride with stoichiometric amounts of acid. The above process involve caustic neutralization with attendant problems.
Another method disclosed for production of N-alkyl substituted morpholine involves the vapor phase cyclic dehydration of a corresponding N-alkyl diethanolamine at 375.degree. C. to 400.degree. C. in the presence of silica-alumina. For example, see I. Ishiguro, E. Kitamura u. H. Matsumura, J. Pharm. Soc. Japan 74, 1162 (1954); C. A. 49, 14767.sup.g (1955). This method suffers from the attendant problem of vapor phase synthesis with low yields and extensive by-product formation. Further, it has been disclosed that amino alcohols such as, for example, di-(2-hydroxypropyl)amine form the corresponding bis-phosphoric acid monoester in the presence of phosphoric acid. See for example U.S. Pat. No. 3,098,072.
It has also been disclosed that N-alkyl morpholines wherein the alkyl moiety contains from 8 to 18 carbon atoms can be produced in liquid phase over an activated alumina catalyst at temperatures that avoid vaporization and decomposition of reagents and products. See for example U.S. Pat. No. 3,641,022.
Unexpectedly, it has been discovered that N-(substituted) morpholine compounds and specifically N-alkyl morpholines and N-(hydroxyalkyl)morpholines can be selectively produced in a single step in liquid phase by use of certain specific catalytically effective substances which are readily available and easily obtained. The selectivity of the instant process to N-(hydroxyalkyl)morpholine compounds is particularly surprising in light of the fact that it has been disclosed that, for example, triethanolamine in the presence of hydrochloric acid yields a myriad of products including the dimorpholinodiethyl ether. In contrast, when using triethanolamine in accordance with the instant process, selective high yield of the N-(2-hydroxyethyl)morpholine compound is produced.